Respiratory masks for protecting the wearer against potentially hazardous contaminants in the air, such as particles, gases and vapours, are well known and are becoming an increasingly important item of personal protection equipment (PPE) in some workplaces to protect personnel against such contaminants that might otherwise endanger their health and safety at work, if inhaled.
Respiratory masks that feel the most comfortable to wear have a facepiece moulded of a soft, compliant rubber formed with an inturned cuff or flap having a feathered edge that forms a hermetic seal against the wearer's facial skin. Such a respiratory mask typically has a fitting in each cheek area for a filter cartridge, and replaceable filter cartridges are typically formed with mating threads which enable them to be screwed into place on the facepiece via cooperative mating threads provided on the cheek areas thereof.
There are many different types of replaceable and disposable filter cartridge known in the art, including those in which the filter media is exposed, at least partially, externally of the cartridge, when in use. However, fully encapsulated filter cartridges are preferred in many working environments as they provide protection for the filter media from damage, particularly in wet conditions. Furthermore, potentially hazardous matter captured by the filter media is protected by the outer, encapsulating cartridge casing, thereby avoiding the risk of skin contamination when the filter cartridge is being removed for checking and/or replacement.
A major consideration in relation to respiratory protective equipment (RPE) is to ensure that the mask fits adequately to the user's face as an inadequate fit will significantly reduce the protection provided to the wearer, and create inward leakages of airborne contaminants. Thus, for RPE to be suitable, it must be matched to the job, the environment, the anticipated airborne contaminant exposure level and, importantly, the wearer. RPE fit testing can be periodically performed on-site by a competent person. However, current health and safety regulations also require a pre-use fit check each time a facepiece is worn and before entering the hazardous environment. This is required to determine if the facepiece has been correctly fitted before a contaminated work area is entered.
The pre-use fit check procedure will vary according to the type of respiratory mask used. In the case of a respiratory mask of the types described above, having replaceable filter cartridges mounted on the cheek areas of the facepiece, which allows the respiratory air to be drawn into the cartridge and through the filter media when a user inhales, and expelled through the cartridge when the user exhales, the pre-use fit check procedure will typically comprise securing the facepiece over the user's nose and mouth, and then sealing the respiratory air flowpath, provided via the cartridge, between the user's nose and mouth and the external environment. The wearer then attempts to inhale, whilst the flowpath is blocked, and this action should cause a vacuum to be created within the facepiece (if the mask is correctly fitted), thereby indicating that the seal between the facepiece and the wearer's face is substantially airtight and, therefore, adequate.
An encapsulated filter cartridge typically comprises a two-part plastic casing, within which the filter media is housed and through which the respiratory air flowpath between the inner facepiece and the external environment is provided. Generally, the housing comprises an inner receptacle and an outer cover which mounted to the inner receptacle such that the open end thereof is covered and the edges of the outer cover extend over the open end edges of the receptacle and substantially parallel to the side walls thereof. The outer cover may be slidably mounted, generally centrally, at the longitudinal edges of the inner receptacle, and spring loaded to bias the cover to a normally “open” position, in which there is a gap between the distal edges of the open end of the receptacle and the outer cover which provides the above-mentioned respiratory air flowpath. When sufficient pressure is applied by the wearer to one end of the outer cover to overcome the spring loaded bias, the cover is caused to slide toward the inner receptacle until it hits the distal edges thereof and, thereby, effectively seals the respiratory air flowpath, whilst the applied pressure remains, in order to enable the above-mentioned pre-use fit check to be performed. When the pressure on the outer cover is removed, it returns to its open configuration for normal use of the mask.
However, there are a number of problems associated with such a known encapsulated filter cartridge. Firstly, the above-described mechanism provided for blocking the air flowpath through the cartridge in order to perform the pre-use fit check, is quite cumbersome and not very user-friendly, requiring significant pressure to be applied by a wearer's whole hand in order to effect the sealing process. Furthermore, the sealing function places the outer cover under significant mechanical stress due to the configuration of the sliding mechanism. Another issue associated with the known encapsulated filter cartridges is that of breathing resistance. It will be known to a person skilled in the art that the lower the breathing resistance of a respiratory mask, the more comfortable it will be for a wearer to breathe normally during use. However, conventional encapsulated filter cartridges typically have quite a high breathing resistance, due to the constricted nature of the airway provided and, therefore, can be quite uncomfortable for use over extended periods of time.